Geology
The Amazon wasn't always like it's now. Ages ago the continents South-America and Africa were one. Is was called 'Pangea'. Pangea splitted about 170 million years ago into two big continents: Laurasia, the northern part and Gondwanaland, the southern part.
The existence of the Amazon goed ways beyond these years The eldest stones in the Amazon are from the Precambrium. The plateaus on the north- and southside of the river use it nowadays as their bottom. These stones are 570 million to 4 billion years old.

When Pangea splitted in Laurasia and Gondwanaland the 'skelleton' of the Amazon was formed. The Andes, where the Amazon River starts, was formed about 65 million years ago. It existed because of the vulcanian activity and the friction in the Earth. All of these happenings are responsible for the shape of the Amazon nowadays.

Because of the friction in the Earth, there where shockwaves, which are to compare with waves on the sea. The depth between the waves formed a huge empty 'bowl' in the East. In the north the the Amazon was higher due to the waves. So made it possible for the water to go from one place to another. Next to this mainstream there were a lot of little river that went their own way. Alle of these rivers together have formed a huge swamp in last couple of 1000 years, which we know as: the Amazon.